Conventionally, a planetary gear mechanism fitted in a vehicular gear casing has been widely known.
For example, Japanese Patent Laying-open No. 2006-183824 describes a planetary gear mechanism including a sun gear, a pinion gear positioned outer than the sun gear and meshing therewith, and a ring gear positioned outer than the pinion gear and meshing therewith. Each pinion gear is rotatably supported by a planetary carrier fitted in the gear casing.
The planetary carrier has a circumference with a plurality of projections and the gear casing has a plurality of recesses to receive the projections. The planetary carrier has the projections fitted into the recesses of the gear casing and is thus fitted in the gear casing.    Patent Document 1: Japanese Patent Laying-open No. 2006-183824